const syb = Symbol('ID')
const syb1 = Symbol.for('ID')
const syb2 = Symbol.for('id')
const syb3 = Symbol.for('id')
const obj = {
    [syb]:'abc',
    [syb1]:'abc'
}
console.log(obj[syb])  //abc
console.log(Object.keys(obj))  //[]
console.log(Object.getOwnPropertySymbols(obj)) //[Symbol('ID')]
console.log(syb === syb1)


// console.log(Symbol.keyFor(syb2))
console.log(syb2 === syb3)
// console.log(syb1 === syb3)

let s1 = Symbol('abc')
let s11 = Symbol.for('abc')
let s2 = Symbol.for('eee')
let s22 = Symbol.for('eee')
let s3 = Symbol.for(123)
let s33 = Symbol.for('123')
let s4 = Symbol.for(0)
let s44 = Symbol.for('0')
console.log(Symbol.keyFor(s1))  //undefined
console.log(Symbol.keyFor(s2))  // eee
console.log(s1 === s11)  //false
console.log(s2 === s22)  //true
console.log(s3 === s33)  //true

console.log(s4 === s44)  //true